1. Field of the Invention
The present invention relates to a liquid droplet ejecting head such as an inkjet head which ejects an ink droplet, and a liquid droplet ejecting device and an image forming apparatus which include the liquid droplet ejecting head.
2. Description of the Related Art
In recent years, an inkjet printer (also referred to as a liquid droplet ejecting device) having inkjet heads (also referred to as liquid droplet ejecting heads) mounted thereon is increasingly used due to its advantages of high quality, low cost, and fast responsiveness (capable of responding to fast printers and slow-and-cheap printers with the number of nozzles being increased or decreased). Amid such trend, demands for further improvement of image quality and further reduction in cost and size are required.
As a method of forming the inkjet head, micro electro-mechanical systems (MEMS) is introduced. This is a micro-fabrication technique using a semiconductor process.
For example, components such as an ink tank, a vibration plate, a piezoelectric element, and an electrode necessary for the inkjet head may be formed on a silicon substrate by processing techniques such as etching and sputtering. However, the head may be made to be smaller in size by decreasing the sizes of the components or studying the arrangement of the components. As a result, many inkjet heads may be obtained from one silicon substrate (semiconductor substrate), and cost may be reduced in accordance with a decrease in size.
In decreasing the size of the inkjet head, it is a crucial issue to compactly mount a driving IC driving the piezoelectric element provided in the inkjet head in addition to the components such as the ink tank, the vibration plate, the piezoelectric element, and the electrode.
FIG. 11 is a diagram illustrating a configuration of an existing inkjet head.
As shown in FIG. 11, the inkjet head of conventional arts includes a head body 200 including a nozzle substrate 201 provided with a nozzle hole ejecting an ink droplet as a liquid droplet, an ink tank substrate 202 provided with an ink tank receiving an ink ejected from the nozzle hole due to a pressure applied thereto with a bending operation of a vibration plate and a piezoelectric element, a liquid supply substrate 203 supplying an ink to the ink tank, and a frame substrate 204; wherein the head body 200 is electrically connected, by soldering or anisotropic conductive film (ACF) bonding, with a flexible printed circuit board (FPC) 206 to which a driving IC 205 for driving the piezoelectric element of the ink tank substrate 202 is bonded. In the inkjet head with this configuration, the FPC 206 oscillates in a flapping manner with the operation of the head, or there is a problem in the strength of the bonding portion between the FPC 206 and the head body. For this reason, handling is not easy and a decrease in size is not realized due to an increase in volume as a whole.
In order to solve such a problem, a configuration is proposed in which a driving IC is mounted on a head body.
For example, Japanese Patent Application Laid-open No. 2005-349712 discloses a configuration in which a partition wall defines the outside of an ink pool chamber (common ink tank) on the layer flush with the ink pool chamber, and a driving IC is disposed in a space provided between a vibration plate and a ceiling plate in the width direction (substrate thickness direction). The driving IC is provided to correspond to each of a plurality of nozzle rows, and is bonded to a metallic interconnection of a piezoelectric element substrate provided with a piezoelectric element through a predetermined height of bump.
Further, Japanese Patent No. 3988042 discloses a configuration in which a sealing substrate is laminated on a passage forming substrate provided with a nozzle with a pressure generating chamber or the like interposed therebetween, and a piezoelectric element is disposed in a space defined from a reservoir (common ink tank) of the sealing substrate. A driving IC is provided to correspond to each of a plurality of nozzle rows, and is bonded to a surface of the sealing substrate located above the piezoelectric element.
Further, Japanese Patent No. 3580363 discloses a configuration in which a driving IC is bonded to a front surface of a bonding member provided in a piezoelectric element holding portion defined from a reservoir (common ink tank) on the layer flush with the reservoir. The driving IC and the piezoelectric element are interconnected to each other through a bonding wire drawn outward from the driving IC and passing through a gap between the reservoir and the piezoelectric element holding portion.